1. Field of the Invention
This invention relates to a sound generator to be incorporated in an electronic musical instrument, and which is capable of varying the nuance of music sound generated in response to the key depression speed and strength.
2. Description of the Prior Art
Recently, the electronic musical instrument has been remakably developed in its sound quality and functions thanks to the introduction of high technology digital systems. There are those electronic musical instruments available in the market, which can generate highly qualified musical sounds very close to those issued by natural musical instruments, and which are provided with higher capability, e.g., of an automatic performance by means of microcomputer technology. The market now tends to continue to demand an appearance of those electonic musical instruments having a higher capability of music expression. As a method of facilitating various music expression, it has been well known that the quality and quantity of sound to be generated can be controlled in reponse to the speed of depression of the key, and the strength of impulse imposed on the key, associated with the initial stage of key depression (hereafter, the latter is to be referred to as the initial touch). For example, in the case of a piano, in which the sound quality is determinable exclusively by the initial touch, it is effective for the electronic musical instrument to simulate the musical sound by this method. Besides the above noted case, there is another case, where the generated sound will be varied in response to the status of the pressure, etc., imposed on the key after having been depressed (hereafter to be referred to as the after touch). This is effective for the electronic musical instrument to simulate the sound of a musical instrument, such as the trumpet, in that both of the quality and quantity of sound can be controlled appropriately even with regard to a constant pitch.
As for those facilitating the initial touch control, there has been proposed a method, in that the generated sound loudness is controlled by a VCA (a voltage control amplifier) in response to the value of detection, e.g., how fast the key is depressed. In this case, however, in spite of its capability of sound loudness control, it is still inadequate, when the electronic musical instrument is to simulate the sound of a piano, in the the timbre of sound is completely changeable depending upon the mode of performance, whether it is played strongly or weakly. There is another attmept proposed, where the generated sound is engaged with timbre control by means or a VCF (a voltage control filter) in response to the speed of key depression, further being controlled as to its loudness by means of a VCA. However, even in this case, it is not feasible to acquire an adequate result in the case of those musical sounds, e.g., associated with a piano performance, in that a variation of the timbre of sound will take place within a wide range depending upon the strength of the impulsive stroke on the leading edge of the sound wave and the subsequently following spectrum construction thereof, in reponse to whether it is played in a strong mood or in a weak mood.
Hereafter, in this invention, the value of detection of the initial touch should be referred to as the touch information.
The control method by means of conventional initial touch, as mentioned previously, in which a VCF and VCA are incorporated, is able to change the timbre and loudness of sound continuously. However, the variation of timbre in this control is simplified too much, on behalf of too much emphasis being placed on continuity of the variation of sound loudness or timbre, resulting in letting the sound generated be short of a natural tune.
An electronic musical instrument with a touch response capability is disclosed in U.S. Pat. No. 4,231,276. This patent proposes that a music sound is synthesized by mixing a complex number of wave-forms of high frequencies having the same basic number of frequencies superposed on different quantities of higher harmonics thereon, the ratio of mixing being changed in response to the touch response signal. This method makes it possible to improve the capability of touch response because the mixing ratio can be specified optionally in response to the degree of touch. However, the quality of sound thus produced cannot exceed the conventional boundary of the musical sound generated by synthesizing from a complex number of wave-forms.
Other prior art references relevant to this invention are given in the following U.S. Pat. Nos.: 3,515,792, 3,854,365, 4,085,648, 4,138,915, 4,224,856, and 4,227,435.